Conventionally, a resin-sealed type semiconductor device and a sealed and airtight type semiconductor device are known as an a semiconductor device housing a packaged semiconductor element.
The resin-sealed type semiconductor device has a structure which embedded directly the semiconductor element mounted in a leadframe in the resin by using a transfer mold etc., and is widely used by the advantage, such as low cost, being suitable for mass production, and a miniaturization being possible.
The sealed and airtight type semiconductor device has a structure which performed in hollow airtight maintenance of the semiconductor element mounted on a base substance composed of insulating materials, such as ceramics. Although the cost is higher compared with the resin-sealed type semiconductor device, the sealed and airtight type semiconductor device is used when high reliability is required because of excellent in airtightness.
In recent years, enlargement, densification, and high integration of a semiconductor element have advanced, and therefore the heating power occurred at the time of operation of the semiconductor element has increased rapidly.
In the sealed and airtight type semiconductor device, it is known about a sealed and airtight type semiconductor device which mounts a semiconductor element directly on the heat radiation body composed of metal.
A copper (Cu) based package can radiate the generated heat satisfactory. On the other hand, warping of the base plate or crack of an alumina substrate had occurred because of thermal expansion difference with the high frequency circuit board made from alumina mounted on a copper (Cu) base plate.
In order to avoid the crack of the alumina substrate, a laminated structure of molybdenum (Mo) and Cu is used, but Mo layer has prevented heat conduction.
Although it is also used as a structure of forming the whole base by a metallic body with the thermal expansion coefficient near that of alumina, such as Mo, and embedding Cu only directly under the semiconductor which is an exothermic unit, a dedicated package must be produced according to the mounting position of the heating element.
In order to control the warping, it is also proposed about a structure which improves a design flexibility both of linear thermal expansion and Young's modulus by increasing the number of laminated layers and fine-tuning to the thickness of each layer finely. However, since there are many numbers of layers, the thickness of each layer is different, and there is a rule also in laminating order, it is easy to occur the mistake at the time of production. Also, according to a system which fine-tunes to the thickness of each layer of multilayered lamination finely, and maintains the warping amount and balance, it is difficult to control the production since there are many parts and products.
In order to avoid the crack of the alumina substrate, a compound material of Mo and Cu is used. The design flexibility of linear thermal expansion and Young's modulus is improved by fine-tuning to the mixing ratio finely. According to the above-mentioned compound material, it is easy to control the production, because of mixing the materials at a material stage. However, a heat conductivity of the compound material is low compared with a pure metal, thereby preventing the heat conduction.